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- Healthy colonized cattle are the major reservoir of Shiga toxin–producing Escherichia coli (STEC) and play a key role in the entry point of the pathogen into the beef chain. Excretion rates and the concentration of the pathogen in feces influence the epidemiology and transmission of the pathogen within herds and to humans. This study evaluated the prevalence and dynamics of fecal shedding of STEC by cattle in a commercial feedlot in Gauteng, South Africa. An initial cross‐sectional survey was conducted; fecal samples were obtained from 106 randomly selected weaned beef calves on arrival at the feedlot using polymerase chain reaction (PCR) to screen by detecting stx1 and stx2 genes. Subsequently, a longitudinal study was conducted, and 15 STEC‐positive and 11 STEC‐negative cattle were sampled monthly and followed to slaughter. STEC O157 and non‐O157 were enumerated in samples using commercial chromogenic agar. Initial prevalence of STEC shedding was 27% (29/106; 95% CI [19, 37%]). All 26 cattle shed STEC intermittently or continuously during the study period, all except one were super‐shedders (≥4 log10 CFU/g) at one or more samplings, and 19 (73%) were persistent or intermittent super‐shedders. Of the 38 STEC isolates recovered, 15 (39%) were serotypeable, representing 11 non‐O157 serogroups, including O101, O168, O178, and O68. The most frequent virulence combination profile was stx1 + eaeA + ehxA (n = 12; 32%). This study confirms the occurrence and variability of STEC super‐shedding in feedlot cattle and highlights that super‐shedding is not limited to STEC O157. It also shows their public health significance.
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- A cross-sectional study was conducted to determine the prevalence, risk factors, and molecular characteristics of Shiga toxin-producing Escherichia coli (STEC) in 12 beef abattoirs in Gauteng province, South Africa. The rela tionship between STEC contamination and aerobic bacterial counts on carcasses at various stages of processing was investigated. Multiplex PCR was used to detect virulence genes in broth-enriched samples, to determine O- serogroups in all samples positive for Shiga toxin-encoding genes (stx), and to characterize isolates of STEC. The overall prevalence of STEC determined by PCR in 419 selective enrichment broth samples was 35.1% (147/419), and was significantly higher (P = 0.037) in perineum hide swabs (50%) than in 24 h chilled carcass swabs (20%). The maximum total aerobic plate count (TAPC) was 3.8 log 2 10 CFU/100 cm for carcass swabs, but was below the South African microbiological standard for meat export at all stages of carcass processing. There was no sig nificant association between TAPC and STEC contamination. Serogroup O113 was the most prevalent serogroup (13.6%; 20/147) detected. Only 33 isolates, all non-O157 STEC, were recovered, amongst which six different genotype combinations were observed. Additionally, the clinically important serogroups O117, O8, and O2 were isolated. Multivariable logistic regression revealed that the odds of STEC contamination was lower in post-wash (OR = 0.42; 95% CI: 0.18–0.98; P = 0.045) and 24 h chilled (OR = 0.33; 95% CI: 0.12–0.91; P = 0.033) carcass swabs compared to pre- and post-evisceration swabs. It was concluded that non-O157 STEC serogroups more frequently colonize beef cattle slaughtered at abattoirs in our study area than O157 STEC, and therefore have a higher potential to enter the food chain during carcass processing, with food safety implications.
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